The invention relates to an active carbon filter unit for a tank system.
For reasons of environmental protection, an escape of hydrocarbon components must be restricted from the fuel container of a tank system which is connected with the ambient atmosphere to balance out different filling levels, temperature fluctuations, evaporations etc. Legal requirements also stipulate a tightness check of the tank system which is to be carried out in an automated manner.
From the document U.S. Pat. No. 6,390,073 B1 a tank system of a motor vehicle is known with an active carbon filter unit which consists of a housing, forming internally two chambers intended to receive active carbon, which are connected with each other via a gap, wherein one chamber is provided with connections for those ducts which are connected with the head space of a fuel container and those which are connected with a suction region of an internal combustion engine. The other chamber, at its end facing away from the gap and with the intermediate arrangement of a first electrically actuatable valve and of a filter, is provided with an air-removal duct leading into the free atmosphere. This first valve is designed as a structural unit which is able to be inserted into a cylindrical recess of the housing and is constructed such that it opens in the idle state and closes when live. It is additionally designed with the requirement that the opening process, which is initiated by a spring, is assisted by the vacuum of the said suction region. A second electrically actuatable valve is situated in the duct which connects the first chamber with the suction region.
During refueling when the engine is not running, the first vale is in the open position, so that air enriched with hydrocarbons can be displaced out of the head space of the fuel container and can escape into the atmosphere via the chambers, containing active carbon, and the filter, with a hydrocarbon component being retained adsorptively. When the engine is running, vice versa the air is drawn in via the filter and the open first valve, wherein in the region of the chambers hydrocarbon components which are still bonded are entrained as a result of desorption and are introduced via the open second valve into the combustion chamber of the engine.
Through the fact that firstly the first and subsequently the second valve are transferred into a closed position, so that the tank system, when the engine is running, is temporarily entirely exposed to the effect of the engine vacuum, a defined underpressure is developed within the tank system, so that the course of the reduction of a differential pressure to the ambient atmosphere provides indications for any unacceptable leakages which may be present.
A feature of this known active carbon filter unit is that to constitute the different forms of operation of aeration and air removal, of flushing and of a tightness check within the tank system a cooperation of structural elements, to be mounted individually, is also necessary outside the active carbon filter unit. In individual cases, this can entail a great effort with regard to installation and in the tightness check, which is ultimately based on a comparison with a standard pressure distribution, it can make costly adjustment operations necessary which are adapted individually to the installation situation. A function check of the cooperating components of the tank system during the air removal operation or a flushing operation and a tightness check can also prove to be comparatively laborious.